A method for solidifying heavy metal contaminated soil based on nickel slag loaded with microorganisms

Abstract

The invention discloses a method for solidifying heavy metal contaminated soil based on nickel slag loaded microorganisms, including: culturing Bacillus pasteurianus bacterial liquid until the optical density OD600 value of the bacterial liquid wavelength at 600nm is 1.8-2.0; 50-100g of urea and 100-120g of CaCl2 are dissolved in deionized water, stirred evenly, and a cementing liquid is obtained; the screened nickel slag particles are added to the cementing liquid, and the nickel slag particles and the cementing liquid are mixed according to a solid-liquid ratio of 2:1-3:1, and a "secondary static stop" method is adopted. After stirring for 5-10min, it is allowed to stand for 3-5min, and a secondary stirring is performed to obtain a reaction solution; the bacterial liquid with an optical density OD600 value of 1.8-2.0 and the reaction solution are injected into the heavy metal contaminated soil body by an intelligent grouting device in turn, until the heavy metal dissolution value meets the specified limit, and the heavy metal contaminated soil is solidified. The heavy metal contaminated soil solidification method of the present invention reduces the activity rate of heavy metals, improves the pH value of the soil, and stimulates the microbial solidification effect for lead and zinc contaminated soil.

Description

Technical Field

[0001] The invention belongs to the technical field of microbial geotechnical engineering, and in particular, relates to a method for solidifying heavy metal contaminated soil based on nickel slag loaded microorganisms, which is suitable for soft soil foundations. Background Art

[0002] Heavy metal pollution is enriched and difficult to degrade in the environment. It is widely distributed in the atmosphere, water, soil, and organisms, threatening the ecological environment and the health of the people. The prevention and control of heavy metal pollution is a long way to go. Among them, lead and zinc pollutants account for 1 / 2 of heavy metal pollutants. Lead and zinc pollutants are typical inorganic pollutants in the soil. They are cumulative poisons and can easily invade human internal organs, causing cancer and other malignant complications, leading to death. Therefore, it is urgent to find an efficient and green method to treat lead and zinc contaminated soil.

[0003] Existing methods for remediating heavy metal contaminated soil are mainly divided into three categories. The first category is physical methods, which is to directly remove heavy metal contaminated soil, but this technology is only suitable for small-scale heavily polluted sites, and the degradation cost is relatively high; the second category is chemical methods, which directly inject chemical reagents into the soil to achieve the treatment effect by reducing and dissolving its metal toxicity. This method is quick to take effect, but it will destroy the soil structure, reduce soil biological activity and soil fertility, etc., and the chemical reagents themselves have corresponding toxicity and there is the generation of toxic by-products; the third category is biological methods, which have the advantages of low cost and low investment. It flexibly uses the root structure of plants in the soil without destroying the site distribution. It has certain economic and ecological benefits and is an ideal method for repairing large-scale, low-level contaminated soil; but there are also technical bottlenecks such as short plants, low biomass, and slow growth of hyperaccumulators; the threat to biodiversity caused by the introduction of hyperaccumulators from other places is also an issue that cannot be ignored.

[0004] The principle of microbial induced calcium carbonate precipitation technology for the remediation of heavy metal contaminated soil is mainly to use MICP technology to make heavy metal ions and carbonate ions react and thus convert into carbonate precipitates. In this process, the main metal pollutants are converted from soluble-exchangeable parts to carbonate parts, which are fixed in the crystal structure, thereby reducing metal toxicity and ion mobility, filling the gaps between soil particles, increasing the cohesion between soil particles, playing a cementing role, and simultaneously achieving the dual goals of controlling heavy metal pollutants and improving soil strength. Compared with existing remediation technologies, it has the following outstanding advantages: (1) wide range of applications, strong applicability, can be used in various geographical locations and environmental conditions including many extreme climate environments, such as salt lakes, acid mine drainage, deserts, glaciers, etc.; (2) wide range of material sources, rich products, can realize the recycling of resources for secondary use; (3) green and environmentally friendly, in line with the principle of low carbon, can effectively avoid secondary pollution and do not destroy the basic structure of the soil; (4) low cost, high efficiency, strong remediation; (5) simple remediation technology and easy operation. Therefore, MICP solidification of heavy metal contaminated soil as a new type of geotechnical material and reinforcement method has brought new opportunities for green environmental protection construction. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method for solidifying heavy metal contaminated soil based on nickel slag loaded with microorganisms. For soft soil foundations contaminated by lead and zinc, the activity rate of heavy metals can be reduced, the pH value of the soil can be improved, and the microbial solidification effect can be stimulated. The heavy metal contaminated soil solidification method can be applied to actual projects, which can effectively improve the stability of the soil foundation, the uniformity, accuracy, autonomous controllability, and energy saving and environmental protection of grouting reinforcement.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme: a method for solidifying heavy metal contaminated soil based on nickel slag loaded with microorganisms, specifically comprising the following steps:

[0007] Step S1, culturing a Bacillus pasteurianus bacterial solution until the optical density OD600 value of the bacterial solution at a wavelength of 600 nm is 1.8 to 2.0;

[0008] Step S2, dissolving 50-100 g of urea and 100-120 g of CaCl2 in deionized water, stirring evenly, to obtain a binder; the concentration of the binder is 0.5 mol / L to 1 mol / L;

[0009] Step S3, adding the screened nickel slag particles to the binder obtained in step S2, mixing the nickel slag particles and the binder according to a solid-liquid ratio of 2:1 to 3:1, adopting a "secondary static stop" method, stirring for 5-10 minutes, standing for 3-5 minutes, and performing secondary stirring to obtain a reaction solution;

[0010] Step S4, injecting the bacterial solution and the reaction solution with an optical density OD600 value of 1.8 to 2.0 into the heavy metal contaminated soil through the intelligent grouting device in turn until the heavy metal dissolution value meets the specified limit, thereby completing the solidification of the heavy metal contaminated soil; the injection amount of the bacterial solution each time is 1 to 1.5 times the pore volume of the soil sample, and the injection amount of the reaction solution each time is 1 to 2 times the pore volume of the soil sample.

[0011] Furthermore, step S1 includes the following sub-steps:

[0012] Step S101, on a sterile operating table, inoculate Bacillus pasteurianus onto a solid culture medium, and invert the solid culture medium in a constant temperature box at 25-35° C. for culturing for 24-48 hours; each liter of the solid culture medium contains 10-20 g / L of tryptone, 1-5 g / L of soy peptone, 1-5 g / L of NaCl, 10-20 g / L of yeast extract, and 10-15 g of agar, and the pH of the solid culture medium is adjusted to 9.0-9.5 by 1-2 mol / L of NaOH solution, and the prepared solid culture medium is placed in a steam cooker at 120-130° C. for sterilization for 10-20 minutes;

[0013] Step S102, selecting milky white colonies from the solid culture medium, adding them to the liquid culture medium, and shaking culture at 25-30° C. until the optical density OD600 value of the bacterial solution at a wavelength of 600 nm is 1.8-2.0; the rotation speed of the shaking culture is 100-150 rpm; each liter of the liquid culture medium contains 10-20 g / L of tryptone, 1-5 g / L of soy peptone, 1-5 g / L of NaCl, and 10-20 g / L of yeast extract, and the pH of the liquid culture medium is adjusted to 9.0-9.5 by 1-2 mol / L NaOH solution, and the prepared liquid culture medium is placed in a steam cooker at 120-130° C. for sterilization for 10-20 min.

[0014] Furthermore, the process of obtaining the screened nickel slag particles is specifically as follows:

[0015] (a) washing the original nickel slag to remove impurities, drying it naturally, and storing it in the open air for 1 to 2 months;

[0016] (b) screening the original nickel slag with a square hole sieve with a diameter of 5 mm to remove silver slag particles larger than 5 mm;

[0017] (c) pouring the retained nickel slag into a particle crushing device, closing the device, and crushing for 5 to 10 minutes;

[0018] (d) obtaining nickel slag particles with different crushing degrees, and packaging them according to particle size distribution by screening method, and retaining nickel slag particles with a particle size less than 0.25 mm.

[0019] Furthermore, the intelligent grouting device includes: a ground-inserted grouting pipe, a soil pressure regulator, an underground connecting distribution pipe, an above-ground connecting distribution pipe, a peristaltic pump, a bacterial liquid storage tank, an above-ground valve button, a constant temperature control device, a reaction liquid storage tank, a liquid volume monitoring device, a base, a remote control, an upper grouting pipe, a lower grouting pipe, and an underground valve twist. The ground-inserted grouting pipe is provided in plurality, each of which is provided with a soil pressure regulator, an upper grouting pipe and a lower grouting pipe are provided on both sides of the ground-inserted grouting pipe, and each of the upper grouting pipe and the lower grouting pipe is provided with an underground valve twist; the top of the ground-inserted grouting pipe is connected to the underground connecting distribution pipe, and the underground connecting distribution pipe is connected to the above-ground connecting The bacteria liquid storage tank and the reaction liquid storage tank are connected with the above-ground connecting distribution pipe, the peristaltic pump is arranged in the above-ground connecting distribution pipe, the bacteria liquid storage tank and the reaction liquid storage tank are respectively connected with the above-ground connecting distribution pipe, the above-ground connecting distribution pipes connecting the bacteria liquid storage tank and the reaction liquid storage tank are both provided with above-ground valve buttons, the bacteria liquid storage tank and the reaction liquid storage tank are both provided with liquid quantity monitoring equipment, the peristaltic pump, the bacteria liquid storage tank, the constant temperature control device, and the reaction liquid storage tank are all arranged on the base; the bacteria liquid storage tank and the reaction liquid storage tank are arranged in the constant temperature control device, and the remote control is respectively connected with the soil pressure regulator, the peristaltic pump, the above-ground valve button, the constant temperature control device, the liquid quantity monitoring equipment, and the underground valve knob.

[0020] Furthermore, the length of the underground grouting pipe is 20m, and the drilling spacing is 1m and the drilling diameter is 0.5m in the upper half of the underground grouting pipe; the drilling spacing is 1.5m and the drilling diameter is 0.8m at 5m from the middle of the underground grouting pipe to the bottom; the drilling spacing is 1.5m and the drilling diameter is 1m at 5m from the bottom of the underground grouting pipe.

[0021] Furthermore, the length of the transverse grouting pipes extending from both sides of the underground grouting pipe is 1.5m, the length of the longitudinal upper grouting pipe and the lower grouting pipe are both 1.0m, and the underground valve is arranged in the middle of the upper grouting pipe and the lower grouting pipe.

[0022] Furthermore, the above-ground valve button and the underground valve button are electromagnetic automatic closing valve buttons.

[0023] Furthermore, the peristaltic pump is a multi-cylinder high-pressure cross-flow peristaltic pump including an online detection system.

[0024] Furthermore, step S4 specifically includes the following sub-steps:

[0025] Step S401, starting the soil pressure regulator, the constant temperature control device, and the liquid volume monitoring device through the remote control switch;

[0026] Step S402, adjusting the constant temperature control device so that the temperature of the bacterial solution and the reaction solution is maintained at 1-5°C;

[0027] Step S403, open the underground valve to control the upper grouting pipe separately;

[0028] Step S404, open the ground valve button for controlling the bacterial solution separately, use a peristaltic pump to inject the bacterial solution into the ground grouting pipe and the upper grouting pipe through the ground connecting distribution pipe and the underground connecting distribution pipe, and control the release amount of the bacterial solution through the soil pressure regulator. After the bacterial solution is injected, let it stand for 6 to 12 hours;

[0029] Step S405, close the ground valve button for controlling the bacterial solution, open the ground valve button for controlling the reaction solution, use a peristaltic pump to inject the reaction solution into the ground grouting pipe and the upper grouting pipe through the ground connecting distribution pipe and the underground connecting distribution pipe, and control the release amount of the reaction solution through the soil pressure regulator. After the grouting is completed, let it stand for 12 to 15 hours;

[0030] Step S406, close the underground valve that controls the upper grouting pipe, and open the underground valve that controls the lower grouting pipe to change the grouting seepage direction;

[0031] Step S407, open the ground valve button for controlling the bacterial solution separately, use a peristaltic pump to inject the bacterial solution into the ground grouting pipe and the lower grouting pipe through the ground connecting distribution pipe and the underground connecting distribution pipe, and control the release amount of the bacterial solution through the soil pressure regulator. After the bacterial solution is injected, let it stand for 6 to 12 hours;

[0032] Step S408, close the ground valve button for controlling the bacterial solution, and open the ground valve button for controlling the reaction solution; use a peristaltic pump to inject the reaction solution into the ground grouting pipe and the lower grouting pipe through the ground connecting and distributing pipes and the underground connecting and distributing pipes, and control the release amount of the reaction solution through the soil pressure regulator. After the grouting is completed, let it stand for 12 to 15 hours;

[0033] Step S409, repeating steps S403 to S408, taking soil samples on site, until the measured heavy metal dissolution value meets the specified limit, and shutting down the intelligent grouting device through the remote control 13.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The nickel slag used in the present invention is a very common material in the waste discharged by industries such as electroplating and smelting. The large amount of nickel slag piled up will cause nickel pollution in the atmosphere, water and soil. At the same time, nickel can enter the human body through the respiratory tract, digestive tract, skin contact and other pathways, and be distributed and accumulated in multiple organs and tissues throughout the body, causing adverse effects on human health. The present invention can improve nickel pollution to a great extent by rationally utilizing nickel slag, and rationally reutilize nickel slag as waste with low cost and high efficiency, and appropriate stimulation can further enhance the use effect of nickel slag;

[0036] (2) The present invention effectively utilizes the good physical properties of nickel slag itself, and takes advantage of the porous structure of nickel slag particles for co-adsorption, providing adsorptive pores suitable for the growth of microorganisms, thereby achieving a loading effect; combined with the technology of microbial induced calcium carbonate precipitation, the nickel slag particles are mixed into the binder, which can make the binder well attached to the pores of the nickel slag particles, inducing the production of more calcium source ions, and producing more carbonate precipitates attached to the surface of the soil in the form of urea hydrolysis, thereby effectively enhancing the strength of the soil, allowing the soil to reach acid-base balance, protecting the soil and maintaining its stable and healthy state. Combined with the technology of microbial induced calcium carbonate to treat heavy metal contaminated soil, the good chemical properties of nickel slag itself are utilized. Due to its own corrosion resistance, it is mixed into the binder, and while acting as an early activator, it can also resist heavy metal erosion, effectively reducing the probability of secondary damage to the soil after repair by heavy metal pollution, and enhancing the stability and durability of the soil after repair;

[0037] (3) The present invention introduces an intelligent grouting device into the heavy metal contaminated soil solidification method, and the steps are simple and reasonable; by controlling the intelligent grouting device with one button, labor costs are saved and the convenience of grouting is improved; by the constant temperature control device, the activity of the slurry is activated to ensure the quality of grouting and improve the efficiency of grouting; by transporting through above-ground and underground distribution pipelines, the accuracy of grouting is improved; by upper and lower grouting pipes, the uniformity of grouting is improved, so as to more effectively reinforce and repair the soil body. The construction steps and methods of the present invention are feasible, saving construction costs, improving construction efficiency, achieving maximum benefits and environmental protection, and are conducive to the further promotion and application of microbial induced calcium carbonate technology to treat heavy metal contaminated soil in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the structure of the soil reinforcement mold:

[0039] Figure 2 This is a schematic diagram of the cross-sectional structure of the intelligent grouting device of the present invention:

[0040] Figure 3 It is a schematic diagram of the cross-sectional structure of the ground-inserted grouting pipe in the present invention;

[0041] Figure 4 It is an operation flow chart of the intelligent grouting device in the present invention;

[0042] Among them, 1-ground inserted grouting pipe; 2-soil pressure regulator; 3-underground connecting distribution pipe; 4-ground connecting distribution pipe; 5-peristaltic pump; 6-bacterial liquid storage tank; 7-ground valve knob; 8-constant temperature control device; 9-reaction liquid storage tank; 10-liquid volume monitoring equipment; 11-base; 13-remote control; 14-upper grouting pipe, 15-lower grouting pipe, 16-underground valve knob. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further explained below in conjunction with the accompanying drawings and embodiments.

[0044] The present invention provides a method for solidifying heavy metal contaminated soil based on nickel slag loaded microorganisms, which produces a good filling effect when the porous structure of nickel slag itself is reasonably used and mixed with microorganisms, and the nickel slag particles play the role of "soil skeleton"; the nickel slag loaded microorganisms react with the calcium source solution to produce more carbonate precipitation and cementation to fill the pores between the contaminated soil particles. Specifically, the following steps are included:

[0045] Step S1, culturing Bacillus pasteurianus bacterial solution until the optical density OD600 value of the bacterial solution at a wavelength of 600nm is 1.8-2.0. When the optical density OD600 is 1.8-2.0, the activity of Bacillus pasteurianus shows an increasing trend. The Bacillus pasteurianus in the present invention has the characteristics of aerobicity, which can promote the catalysis of high-yield urease under urea hydrolysis. Its role in the solidification process of heavy metal contaminated soil is: 1) providing urease for urea hydrolysis; 2) providing nucleation points for the deposition of calcium carbonate crystals. Bacillus pasteurianus is non-toxic and harmless, green and low-carbon, and is widely present in soil, fertilizer, and water environments. At the same time, it also has strong biological activity in harsh soil environments such as acid, alkali, and high salt, avoiding secondary pollution of the land. Specifically including the following sub-steps:

[0046] Step S101, on a sterile operating table, inoculate Bacillus pasteurianus onto a solid culture medium, and invert the solid culture medium in a constant temperature box at 25-35° C. for 24-48 hours to activate Bacillus pasteurianus; each liter of the solid culture medium contains 10-20 g / L of tryptone, 1-5 g / L of soy peptone, 1-5 g / L of NaCl, 10-20 g / L of yeast extract, and 10-15 g of agar, and the pH of the solid culture medium is adjusted to 9.0-9.5 by 1-2 mol / L of NaOH solution, and the prepared solid culture medium is placed in a steam cooker at 120-130° C. for sterilization for 10-20 minutes;

[0047] Step S102, selecting milky white colonies from the solid culture medium, adding them to the liquid culture medium, and shaking culture at 25-30° C. until the optical density OD600 value of the bacterial solution at a wavelength of 600 nm is 1.8-2.0; the rotation speed of the shaking culture is 100-150 rpm, and the shaking culture time is not less than 48 hours; each liter of the liquid culture medium contains 10-20 g / L of tryptone, 1-5 g / L of soy peptone, 1-5 g / L of NaCl, and 10-20 g / L of yeast extract, and the pH of the liquid culture medium is adjusted to 9.0-9.5 by 1-2 mol / L NaOH solution, and the prepared liquid culture medium is placed in a steam cooker at 120-130° C. for sterilization for 10-20 min.

[0048] Step S2, dissolving 50-100g of urea and 100-120g of CaCl2 in deionized water, stirring evenly to obtain a cementing solution, the concentration of the cementing solution is 0.5mol / L-1mol / L; CaCl2 is selected as a calcium source for the preparation of the cementing solution. CaCl2 provides higher urease activity and more calcite in the entire urea hydrolysis process, which can better stimulate the activity of the cementing solution, thereby achieving the best grouting effect and the best degree of soil solidification.

[0049] Step S3, adding the screened nickel slag particles into the binder liquid obtained in step S2, the nickel slag particles and the binder liquid are mixed at a solid-liquid ratio of 2:1 to 3:1, and a "secondary static stop" method is adopted. After stirring for 5-10 minutes, the mixture is allowed to stand for 3 to 5 minutes, and a secondary stirring is performed to obtain a reaction liquid. This can make the stirring more uniform, the binder liquid can better adhere to the pores of the nickel slag, and the loading effect is better.

[0050] The process of obtaining the screened nickel slag particles in the present invention is specifically as follows:

[0051] (a) washing the original nickel slag to remove impurities, drying it naturally, and storing it in the open air for 1 to 2 months;

[0052] (b) The original nickel slag is screened with a square hole sieve with a diameter of 5 mm to remove the silver slag particles larger than 5 mm.

[0053] (c) pouring the retained nickel slag into a particle crushing device, closing the device, and crushing for 5 to 10 minutes;

[0054] (d) obtaining nickel slag particles with different crushing degrees, and packaging them according to particle size distribution by screening method, and retaining nickel slag particles with a particle size less than 0.25 mm.

[0055] Step S4, injecting the bacterial solution and the reaction solution with an optical density OD600 value of 1.8 to 2.0 into the heavy metal contaminated soil in turn through the intelligent grouting device until the heavy metal dissolution value meets the specified limit, and the heavy metal contaminated soil is solidified. The bacterial solution itself can produce urease, which catalyzes the urea hydrolysis reaction, and carbonate ions will be generated around the bacterial solution; the surface of the bacterial solution is negatively charged, and calcium chloride, i.e., calcium source ions, from the cementing solution are adsorbed to produce calcium carbonate precipitation attached to the surface of the soil, which has the effect of reinforcing the soil; and due to the porous structure of the nickel slag fragments, the calcium source ions in the cementing solution can be attached to its pores, which has the effect of "primary reinforcement"; due to the chemical properties of the nickel slag fragments themselves, the cementing solution mixed with nickel slag can induce the production of more calcium source ions after the urea hydrolysis reaction, so that more calcium carbonate precipitation is attached to the soil, thereby playing a "secondary reinforcement" role, enhancing the strength of the soil, and achieving the purpose of treating heavy metal contaminated soil. The present invention improves the uniformity of bacterial liquid grouting and reaction liquid grouting through an intelligent grouting device, improves the overall solidification effect of contaminated soil, and provides more accurate data for subsequent detection of heavy metal concentration values ​​in soil. Each injection of bacterial liquid is 1 to 1.5 times the pore volume of the soil, and each injection of reaction liquid is 1 to 2 times the pore volume of the soil, so as to promote full reaction between slurry and soil and ensure good solidification effect of soil.

[0056] like Figure 2The intelligent grouting device of the present invention comprises: a ground-inserted grouting pipe 1, a soil pressure regulator 2, an underground connecting distribution pipe 3, an above-ground connecting distribution pipe 4, a peristaltic pump 5, a bacterial liquid storage tank 6, an above-ground valve button 7, a constant temperature control device 8, a reaction liquid storage tank 9, a liquid volume monitoring device 10, a base 11, a remote control 13, an upper grouting pipe 14, a lower grouting pipe 15, and an underground valve twist 16; a plurality of ground-inserted grouting pipes 1 are provided, and each ground-inserted grouting pipe 1 is provided with a soil pressure regulator 2. As the soil deepens, the pressure increases dramatically, and the grouting amount required for each depth is also very different. The grouting amount is adjusted by setting the soil pressure regulator 2; upper grouting pipes 14 and lower grouting pipes 15 are provided on both sides of the ground-inserted grouting pipe 1, and each upper grouting pipe 14 and lower grouting pipe 15 is provided with an underground valve twist 16. The uniformity of grouting at both ends of the soil is achieved by adjusting the underground valve twist 16; the top of the ground-inserted grouting pipe 1 is connected to the underground connecting distribution pipe 3 , the underground connecting distribution pipe 3 is connected with the ground connecting distribution pipe 4, the peristaltic pump 5 is arranged in the ground connecting distribution pipe 4, the bacteria liquid storage tank 6 and the reaction liquid storage tank 9 are respectively connected with the ground connecting distribution pipe 4, and the ground connecting distribution pipe 4 connecting the bacteria liquid storage tank 6 and the reaction liquid storage tank 9 is provided with a ground valve button 7, the bacteria liquid storage tank 6 and the reaction liquid storage tank 9 are provided with a liquid quantity monitoring device 10, the peristaltic pump 5, the bacteria liquid storage tank 6, the constant temperature control device 8, and the reaction liquid storage tank 9 are all arranged on the base 11, the bacteria liquid storage tank 6 and the reaction liquid storage tank 9 are arranged in the constant temperature control device 8, and the temperature of the liquid in the bacteria liquid storage tank 6 and the reaction liquid storage tank 9 is maintained at 1-5°C by the constant temperature control device; the remote control 13 is respectively connected with the soil pressure regulator 2, the peristaltic pump 5, the ground valve button 7, the constant temperature control device 8, the liquid quantity monitoring device 10, and the underground valve knob 16, and the remote control 13 is used to realize the control and adjustment of the intelligent grouting device.

[0057] like Figure 3 In the present invention, the ground-inserted grouting pipe 1 is made of fiber material and has a length of 20m. As the depth of the soil increases, the soil pressure gradually increases. Therefore, the diameter of the holes drilled on the ground-inserted grouting pipe 1 needs to increase with the depth of the soil. The upper half of the ground-inserted grouting pipe 1 is set with a drilling spacing of 1m and a drilling diameter of 0.5m; the middle part of the ground-inserted grouting pipe 1 is extended to 5m from the bottom and the drilling spacing is 1.5m, and the drilling diameter is 0.8m; the bottom 5m of the ground-inserted grouting pipe 1 is set with a drilling spacing of 1.5m and a drilling diameter of 1m. The transverse grouting pipes extending from both sides of the underground grouting pipe 1 are made of carbon steel and are 1.5 m long. The longitudinal upper grouting pipe 14 and the lower grouting pipe 15 are both 1.0 m long. The underground valve button 16 is arranged in the middle of the upper grouting pipe 14 and the lower grouting pipe 15, and the underground valve button 16 is used to achieve uniform grouting of the upper grouting pipe 14 and the lower grouting pipe 15.

[0058] The soil pressure regulator 2 in the present invention is made of alloy steel, which has the advantages of high toughness, wear resistance, corrosion resistance, etc. The surface of the soil pressure regulator 2 can be coated with waterproof material to ensure that it is not disturbed by liquid spraying during use, thereby accurately detecting the soil pressure and achieving its durability and long-term effectiveness in the soil.

[0059] The above-ground connecting and distributing pipe 4 of the present invention is made of LLDPE linear low-density polyethylene. Compared with general polyethylene materials, LLDPE has excellent environmental stress cracking resistance and electrical insulation, high heat resistance, impact resistance and puncture resistance, etc., and is suitable for long-term exposure to the outdoors, thereby improving the long-term durability of the overall device. The underground connecting and distributing pipe 3, the upper grouting pipe 14, and the lower grouting pipe 15 of the present invention are all made of carbon steel, and each interface is connected by a flange, which is convenient for later disassembly and maintenance.

[0060] In the present invention, the above-ground valve button 7 and the underground valve button 16 are electromagnetic automatic closing valve buttons, and the material thereof is selected from ferritic stainless steel, because it contains 15%-30% chromium element, and its corrosion resistance, toughness and weldability are improved with the increase of chromium content, and its chloride stress corrosion resistance is better than other types of stainless steel. The above-ground valve button 7 can realize the principle of distributed grouting, and accurately control the direct grouting; the underground valve button 16 can control the "two-end grouting", and the peristaltic pump 5 can realize the "pressure increase" process, and accurately control the grouting uniformity.

[0061] The peristaltic pump 5 in the present invention is a multi-cylinder high-pressure cross-flow peristaltic pump with an online detection system, which is connected to the bacterial solution, the reaction solution and the soil respectively. The peristaltic pump 5 can perform real-time detection, detect the pipeline flowability and the directness of the grouting, so as to ensure the effectiveness of the grouting; its multi-cylinder high-pressure characteristics can greatly improve the impact and remoteness of the grouting, and ensure the quality and quantity of the grouting cycle.

[0062] The thermostatic control device 8 in the present invention will adopt a "degassing hood type" thermostatic control device, which generates electricity by connecting to underground pipelines, and its temperature adjustment is controlled by a remote control device. The "degassing hood type" is based on the principle of effectively isolating interfering factors such as water, oxygen, and carbon dioxide in the gas to ensure that the bacterial liquid and the reaction liquid placed in the device are not contaminated, thereby improving the grouting quality. The thermostatic control is based on the principle of controlled heat and cold and constant temperature, which can accurately and long-term directly control the ambient temperature of the grouting liquid, in order to activate bacterial activity, boost the corrosion resistance of nickel slag, and maintain the function of the reinforcement liquid, thereby achieving the optimal grouting effect.

[0063] In the present invention, the bacterial liquid storage tank 6 and the reaction liquid storage tank 9 are both made of PE plastic material, which has excellent low-temperature resistance, the lowest operating temperature can reach -100 to -70°C, good chemical stability, and can withstand the corrosion of most acids and alkalis; it is insoluble in general solvents at room temperature, has low water absorption, and excellent electrical insulation; its material can well contact and absorb the temperature transmitted from the outside, so that the bacterial liquid in the bacterial liquid storage tank 6 and the reaction liquid in the reaction liquid storage tank 9 are better activated; its milky white style makes it easy to observe the amount of liquid used, realizing monitoring and visualization in one.

[0064] The liquid quantity monitoring device 10 of the present invention is made of PE plastic material, which has strong corrosion resistance, so as to achieve long-term use. It can still maintain flexibility at low temperatures and has high electrical insulation. Its melting point is between 130 and 145°C. The liquid quantity monitoring device 10 can accurately monitor the remaining amount of grouting liquid at any time. If the liquid remaining amount reaches a certain index, it will be transmitted to the remote control through a signal to remind and warn, so as to ensure that the entire grouting process is accurate, complete and correct.

[0065] like Figure 4 The present invention adopts the "two-end grouting, pressure increasing" process through the grouting process of the intelligent grouting device, that is: open the upper grouting pipe 14, close the lower grouting pipe 15, and inject the bacterial solution and the reaction liquid into the upper end of the soil in sequence; then close the upper grouting pipe 14, open the lower grouting pipe 15, and inject the bacterial solution and the reaction liquid into the lower end of the soil in sequence, and adjust the grouting pressure value of the peristaltic pump 5 to increase each round, so as to solve the problem that the calcium carbonate precipitation measured after reinforcement is mainly concentrated on the top of the soil sample due to the traditional "one-way grouting" method, and the purpose is to achieve the uniformity of grouting and improve the overall solidification effect of the contaminated soil. It specifically includes the following sub-steps:

[0066] Step S401, starting the soil pressure regulator 2, the constant temperature control device 8, and the liquid volume monitoring device 10 through the remote control switch 13;

[0067] Step S402, adjusting the constant temperature control device 8 so that the temperature of the bacterial liquid and the reaction liquid is maintained at 1-5°C, thereby ensuring the activity of the injected slurry;

[0068] Step S403, separately open the underground valve of the upper grouting pipe 14 to make the grouting flow direction from top to bottom;

[0069] Step S404, open the ground valve button for controlling the bacterial solution separately, use the peristaltic pump 5 to inject the bacterial solution into the ground grouting pipe 1 and the upper grouting pipe 14 through the ground connecting distribution pipe 4 and the underground connecting distribution pipe 3, and the soil pressure regulator 2 controls the release amount of the bacterial solution to make the soil and the bacterial solution undergo an initial microbial solidification reaction. After the bacterial solution is injected, let it stand for 6 to 12 hours; if the bacterial solution remaining in the bacterial solution storage tank 6 is insufficient, the liquid amount monitoring device 10 on the bacterial solution storage tank 6 will automatically remind;

[0070] Step S405, close the ground valve button for controlling the bacterial solution, and open the ground valve button for controlling the reaction solution; use the peristaltic pump 5 to inject the reaction solution into the ground grouting pipe 1 and the upper grouting pipe 14 through the ground connecting distribution pipe 4 and the underground connecting distribution pipe 3; the soil pressure regulator 2 controls the release amount of the reaction solution so that it mixes with the added bacterial solution to produce calcium carbonate precipitation and solidify around the soil; after the grouting is completed, let it stand for 12 to 15 hours to allow it to fully react; if the reaction solution in the reaction solution storage tank 9 is insufficient, the liquid amount monitoring device 10 on the reaction solution storage tank 9 will automatically remind;

[0071] Step S406, close the underground valve that controls the upper grouting pipe 14, and open the underground valve that controls the lower grouting pipe 15 to change the grouting seepage direction from bottom to top;

[0072] Step S407, open the ground valve button for controlling the bacterial solution separately, use the peristaltic pump 5 to inject the bacterial solution into the ground grouting pipe 1 and the lower grouting pipe 15 through the ground connecting distribution pipe 4 and the underground connecting distribution pipe 3, and the soil pressure regulator 2 controls the release amount of the bacterial solution. After the bacterial solution is injected, let it stand for 6 to 12 hours; if the bacterial solution remaining in the bacterial solution storage tank 6 is insufficient, the liquid amount monitoring device 10 on the bacterial solution storage tank 6 will automatically remind;

[0073] Step S408, close the ground valve button that controls the bacterial liquid, and open the ground valve button that controls the reaction liquid; use the peristaltic pump 5 to inject the reaction liquid into the ground grouting pipe 1 and the lower grouting pipe 15 through the ground connecting distribution pipe 4 and the underground connecting distribution pipe 3, and the soil pressure regulator 2 controls the release amount of the reaction liquid. After the grouting is completed, let it stand for 12 to 15 hours to allow it to fully react; if the reaction liquid in the reaction liquid storage tank 9 is insufficient, the liquid amount monitoring device 10 on the reaction liquid storage tank 9 will automatically remind. Grouting at both ends is completed, which is recorded as a round of grouting reinforcement of the soil. In each round, the grouting pressure value of the peristaltic pump 5 is increased by remote control 13 to increase the impact force of the slurry seepage, so that the liquid fully fills the soil pores and the soil solidifies evenly.

[0074] Step S409, repeating steps S403 to S408, taking soil samples on site, and measuring the heavy metal dissolution value to meet the specified limit, that is, the solidification / stabilization of heavy metals in the contaminated soil meets the requirements, and closing the automatic grouting device through the remote control 13.

[0075] The integrity of the overall grouting is ensured by the above-mentioned intelligent grouting device process. It has a simple operation method, precise control of the operation links, continuous operation steps, and can save manpower and material resources on a large scale.

[0076] In order to provide more powerful experimental data support for the use of MICP technology in treating heavy metal contaminated soil, indoor experiments were carried out to study the optimal binder concentration, the solid-liquid ratio of nickel slag particles to binder, the injection volume of bacterial solution and the injection volume of reaction solution; the indoor test device corresponds to the intelligent grouting device and the grouting process is consistent. The results obtained are provided for reference and application in actual on-site projects.

[0077] In the present invention, the soil reinforcement mold adopts the "layered grouting method" and "grouting at both ends, pressure increasing" process for repeated grouting. In order to ensure the demoulding and water permeability of the sample, the test mold body is selected with a diameter of Transparent plexiglass tube with height h = 80 mm, such as Figure 1 The reinforcement mold in the present invention includes a cylinder I101, a cylinder II 102, an upper grouting pipe 103, a bolt 104, a 39.1mm*80mm cylinder 105, a lower grouting pipe 106, a bottom support 107, an annular groove 108, a bolt hole 109, a vent hole 110, an upper grouting pipe valve twist 111, and a lower grouting pipe valve twist 112. Cylinder I101, cylinder II102, upper grouting pipe 103, annular groove 108, and vent 110 are integrated molds, and cylinder I101, cylinder II102, lower grouting pipe 106, annular groove 108, and vent 110 are integrated molds to form a sample cap; upper grouting pipe 103 and lower grouting pipe 106 are connected to a peristaltic pump, and the "two-end grouting, pressure increase" process is realized by controlling and adjusting the upper grouting pipe valve twist 111, the lower grouting pipe valve twist 112, and the peristaltic pump grouting pressure value. The specific grouting process of the reinforced mold is the same as the grouting process of the intelligent grouting device. The reinforced mold is used to study the optimal binder concentration, the solid-liquid ratio of nickel slag particles to binder, the bacterial liquid injection amount, and the reaction liquid injection amount in the heavy metal contaminated soil solidification method.

[0078] Example 1

[0079] This embodiment provides a method for solidifying heavy metal contaminated soil based on nickel slag loaded with microorganisms, which specifically includes the following steps:

[0080] Step S1, culturing the Bacillus pasteurianus bacterial solution until the optical density OD600 value of the bacterial solution at a wavelength of 600nm is 1.952; specifically,

[0081] Step S101, on a sterile operating table, inoculate Bacillus pasteurianus onto a solid culture medium, and invert the solid culture medium in a 35°C constant temperature incubator for 48 hours to activate Bacillus pasteurianus; each liter of the solid culture medium contains 20 g / L of tryptone, 5 g / L of soy peptone, 5 g / L of NaCl, 20 g / L of yeast extract, and 15 g of agar, and the pH of the solid culture medium is adjusted to 9.0 by 1 mol / L of NaOH solution, and the prepared solid culture medium is placed in a steam cooker at 121°C for sterilization for 20 minutes;

[0082] Step S102, selecting milky white colonies from the solid culture medium, adding them to the liquid culture medium, shaking and culturing at 30°C, and the optical density OD600 value of the bacterial solution at a wavelength of 600nm is 1.952; the rotation speed of the shaking culture in this embodiment is 130rpm, and the shaking culture time is 48h; each liter of the liquid culture medium contains 20g / L tryptone, 5g / L soy peptone, 5g / L NaCl, and 20g / L yeast extract, and the pH of the liquid culture medium is adjusted to 9.0 by 1mol / L NaOH solution, and the prepared liquid culture medium is placed in a steam cooker at 121°C for sterilization for 20min.

[0083] Step S2, dissolving 100 g of urea and 120 g of CaCl2 in deionized water, stirring evenly, to obtain a 1 mol / L cementing solution;

[0084] Step S3, adding the screened nickel slag particles to the binder obtained in step S2, the nickel slag particles and the binder are mixed at a solid-liquid ratio of 2.78:1, and a "secondary static stop" method is adopted. After stirring for 10 minutes, wait for 3 minutes, and perform secondary stirring to obtain a reaction solution;

[0085] The process of obtaining the screened nickel slag particles in this embodiment is specifically as follows:

[0086] (a) washing the original nickel slag to remove impurities, drying it naturally, and storing it in the open air for 2 months;

[0087] (b) screening the original nickel slag with a square hole sieve with a diameter of 5 mm to remove silver slag particles larger than 5 mm;

[0088] (c) pouring the retained nickel slag into a particle crushing device, closing the device, and crushing for 5 minutes;

[0089] (d) obtaining nickel slag particles with different crushing degrees, and packaging them according to particle size distribution by screening method, and retaining nickel slag particles with a particle size less than 0.25 mm.

[0090] Step S4, inject the bacterial solution with an optical density OD600 value of 1.952 and the reaction solution into the heavy metal contaminated soil through the indoor test reinforcement mold in turn until the heavy metal dissolution value meets the specified limit, and the heavy metal contaminated soil is solidified; specifically, the amount of bacterial solution injected each time is 1.5 times the pore volume of the soil sample, the grouting speed is 1.5mL / min, and the grouting is left to stand for 6 hours; the amount of reaction solution injected each time is 1.5 times the pore volume of the soil sample, the grouting speed is 1.5mL / min, and the grouting is left to stand for 6 hours; after one bacterial solution grouting and one reaction solution grouting are completed, keep the soil column at 25℃ for 12 hours, change the seepage direction of the grouting and repeat the above grouting process. The completion of grouting at the upper and lower ends is recorded as one round, and the setting value of the grouting pressure in each round is increasing. The number of grouting rounds is 12 rounds, and the soil sample is cleaned with deionized water, the mold is removed, and the curing is carried out for 28 days to obtain the solidified heavy metal contaminated soil.

[0091] The heavy metal contaminated soil solidification method of this embodiment allows microorganisms to better attach to the pores of nickel slag, providing a more effective reaction liquid for subsequent soil reinforcement; the indoor test reinforcement mold is matched with the on-site intelligent grouting device, which can simply and efficiently implement the steps of "grouting at both ends and increasing pressure", so as to achieve uniform grouting and optimal soil reinforcement effect, increase the accuracy of the test results, and enhance the data reference for on-site engineering applications.

[0092] Example 2

[0093] This embodiment provides a method for solidifying heavy metal contaminated soil based on nickel slag loaded with microorganisms, which specifically includes the following steps:

[0094] Step S1, culturing a Bacillus pasteurianus bacterial solution until the optical density OD600 value of the bacterial solution at a wavelength of 600 nm is 1.8; specifically,

[0095] Step S101, on a sterile operating table, inoculate Bacillus pasteurianus onto a solid culture medium, and invert the solid culture medium in a 25°C constant temperature incubator for 24 hours to activate the Bacillus pasteurianus; each liter of the solid culture medium contains 10 g / L of tryptone, 1 g / L of soy peptone, 1 g / L of NaCl, 10 g / L of yeast extract, and 10 g of agar, and the pH of the solid culture medium is adjusted to 9.5 by 2 mol / L of NaOH solution, and the prepared solid culture medium is placed in a 120°C steam cooker for sterilization for 20 minutes;

[0096] Step S102, select milky white colonies from the solid culture medium, add them to the liquid culture medium, shake and culture at 25°C, and the optical density OD600 value of the bacterial solution at a wavelength of 600nm is 1.8; the rotation speed of the shaking culture in this embodiment is 100rpm, and the shaking culture time is 72h; each liter of the liquid culture medium contains 10g / L tryptone, 1g / L soy peptone, 1g / L NaCl, and 10g / L yeast extract, and the pH of the liquid culture medium is adjusted to 9.0 by 2mol / L NaOH solution, and the prepared liquid culture medium is placed in a steam cooker at 130°C for sterilization for 10min.

[0097] Step S2, dissolving 50 g of urea and 100 g of CaCl2 in deionized water, stirring evenly, to obtain a 0.5 mol / L cementing solution;

[0098] Step S3, adding the screened nickel slag particles to the binder obtained in step S2, the nickel slag particles and the binder are mixed at a solid-liquid ratio of 2:1, and a "secondary static stop" method is adopted. After stirring for 10 minutes, the mixture is allowed to stand for 5 minutes, and a secondary stirring is performed to obtain a reaction solution;

[0099] The process of obtaining the screened nickel slag particles in this embodiment is specifically as follows:

[0100] (a) washing the original nickel slag to remove impurities, drying it naturally, and storing it in the open air for 1 month;

[0101] (b) screening the original nickel slag with a square hole sieve with a diameter of 5 mm to remove silver slag particles larger than 5 mm;

[0102] (c) pouring the retained nickel slag into a particle crushing device, closing the device, and crushing for 10 minutes;

[0103] (d) obtaining nickel slag particles with different crushing degrees, and packaging them according to particle size distribution by screening method, and retaining nickel slag particles with a particle size less than 0.25 mm.

[0104] Step S4, inject the bacterial solution with an optical density OD600 value of 1.8 and the reaction solution into the heavy metal contaminated soil body in turn through the indoor test reinforcement mold until the heavy metal dissolution value meets the specified limit, and the heavy metal contaminated soil is solidified; specifically, the amount of bacterial solution injected each time is 1 times the pore volume of the soil sample, the grouting speed is 1.5mL / min, and the grouting is left to stand for 12h after completion; the amount of reaction solution injected each time is 2 times the pore volume of the soil sample, the grouting speed is 1.5mL / min, and the grouting is left to stand for 12h after completion; after one bacterial solution grouting and one reaction solution grouting are completed, keep the soil column at 25℃ for 15h, change the seepage direction of the grouting and repeat the above grouting process. The completion of grouting at the upper and lower ends is recorded as one round, and the setting value of the grouting pressure in each round is increasing. The number of grouting rounds is 10 rounds, and the soil sample is cleaned with deionized water, the mold is removed, and the curing is carried out for 28 days to obtain the solidified heavy metal contaminated soil.

[0105] The heavy metal contaminated soil solidification method of this embodiment allows microorganisms to better attach to the pores of nickel slag, providing a more effective reaction liquid for subsequent soil reinforcement; the indoor test reinforcement mold is matched with the on-site intelligent grouting device, which can simply and efficiently implement the steps of "grouting at both ends and increasing pressure", so as to achieve uniform grouting and optimal soil reinforcement effect, increase the accuracy of the test results, and enhance the data reference for on-site engineering applications.

[0106] Example 3

[0107] This embodiment provides a method for solidifying heavy metal contaminated soil based on nickel slag loaded with microorganisms, which specifically includes the following steps:

[0108] Step S1, culturing a Bacillus pasteurianus bacterial solution until the optical density OD600 value of the bacterial solution at a wavelength of 600 nm is 2.0; specifically,

[0109] Step S101, on a sterile operating table, inoculate Bacillus pasteurianus onto a solid culture medium, and invert the solid culture medium in a 30°C constant temperature incubator for 48 hours to activate Bacillus pasteurianus; each liter of the solid culture medium contains 15 g / L of tryptone, 5 g / L of soy peptone, 1 g / L of NaCl, 15 g / L of yeast extract, and 15 g of agar, and the pH of the solid culture medium is adjusted to 9.5 by 1 mol / L of NaOH solution, and the prepared solid culture medium is placed in a steam cooker at 130°C for sterilization for 10 minutes;

[0110] Step S102, select milky white colonies from the solid culture medium, add them to the liquid culture medium, shake and culture at 30°C, and the optical density OD600 value of the bacterial solution at a wavelength of 600nm is 2.0; the rotation speed of the shaking culture in this embodiment is 150rpm, and the shaking culture time is 48h; each liter of the liquid culture medium contains 20g / L tryptone, 5g / L soy peptone, 5g / L NaCl, and 20g / L yeast extract, and the pH of the liquid culture medium is adjusted to 9.5 by 1mol / L NaOH solution, and the prepared liquid culture medium is placed in a steam cooker at 130°C for sterilization for 20min.

[0111] Step S2, dissolving 100 g of urea and 100 g of CaCl2 in deionized water, stirring evenly, to obtain a 0.75 mol / L cementing solution;

[0112] Step S3, adding the screened nickel slag particles to the binder obtained in step S2, the nickel slag particles and the binder are mixed at a solid-liquid ratio of 3:1, and the mixture is stirred for 5 minutes and then allowed to stand for 5 minutes by a "secondary static stop" method, and stirred twice to obtain a reaction solution;

[0113] The process of obtaining the screened nickel slag particles in this embodiment is specifically as follows:

[0114] (a) washing the original nickel slag to remove impurities, drying it naturally, and storing it in the open air for 1 month;

[0115] (b) screening the original nickel slag with a square hole sieve with a diameter of 5 mm to remove silver slag particles larger than 5 mm;

[0116] (c) pouring the retained nickel slag into a particle crushing device, closing the device, and crushing for 10 minutes;

[0117] (d) obtaining nickel slag particles with different crushing degrees, and packaging them according to particle size distribution by screening method, and retaining nickel slag particles with a particle size less than 0.25 mm.

[0118] Step S4, inject the bacterial solution with an optical density OD600 value of 2.0 and the reaction solution into the heavy metal contaminated soil body in turn through the indoor test reinforcement mold until the heavy metal dissolution value meets the specified limit, and the heavy metal contaminated soil is solidified; specifically, the amount of bacterial solution injected each time is 1.5 times the pore volume of the soil sample, the grouting speed is 1.5mL / min, and the grouting is left to stand for 10 hours; the amount of reaction solution injected each time is 1 times the pore volume of the soil sample, the grouting speed is 1.5mL / min, and the grouting is left to stand for 10 hours; after one bacterial solution grouting and one reaction solution grouting are completed, keep the soil column at 25℃ for 15 hours, change the seepage direction of the grouting and repeat the above grouting process. The completion of grouting at the upper and lower ends is recorded as one round, and the setting value of the grouting pressure in each round is increasing. The number of grouting rounds is 15 rounds, and the soil sample is cleaned with deionized water, the mold is removed, and the curing is carried out for 28 days to obtain the solidified heavy metal contaminated soil.

[0119] The heavy metal contaminated soil solidification method of this embodiment allows microorganisms to better attach to the pores of nickel slag, providing a more effective reaction liquid for subsequent soil reinforcement; the indoor test reinforcement mold is matched with the on-site intelligent grouting device, which can simply and efficiently implement the steps of "grouting at both ends and increasing pressure", so as to achieve uniform grouting and optimal soil reinforcement effect, increase the accuracy of the test results, and enhance the data reference for on-site engineering applications.

[0120] Example 4

[0121] In this embodiment, the solid-liquid ratio of nickel slag particles to the binder liquid is adjusted through indoor experiments on the basis of embodiment 1, and the unconfined compressive strength of the contaminated soil treated by microbial solidification is tested. The test results are shown in Table 1:

[0122] Table 1: Effect of solid-liquid ratio of nickel slag particles to binder on unconfined compressive strength

[0123]

[0124] As shown in Table 1, when the solid-liquid ratio of nickel slag particles to the binder is 2:1 to 3:1, the unconfined compressive strength of the contaminated soil treated by microbial solidification first increases, and when the solid-liquid ratio is 2.78:1, the unconfined compressive strength reaches a maximum value of 580.6Mpa. When the solid-liquid ratio is 3:1, the unconfined compressive strength decreases slightly, and the decrease value is only 2.3Mpa. It can be regarded that the soil strength fluctuates slightly within a stable range, and the impact is small and can be ignored. In the above solid-liquid ratio, the nickel slag loading effect is optimal, and the soil solidification effect is excellent. When the solid-liquid ratio of nickel slag particles to the binder is greater than 3:1, the unconfined compressive strength of the contaminated soil treated with microbial solidification decreases significantly. This is because the increase in the nickel slag content causes the soil structure to become denser, and the soil expansion coefficient also increases, resulting in lower strength; when the solid-liquid ratio of nickel slag particles to the binder is less than 2:1, due to the low nickel slag incorporation ratio, the binder cannot adhere to it well, and thus cannot produce more calcium source ions, affecting the effect of soil reinforcement.

[0125] Example 5

[0126] In this embodiment, the concentration of the cementing fluid was adjusted through indoor experiments on the basis of embodiment 1, and the unconfined compressive strength of the contaminated soil treated by microbial solidification was tested. The test results are shown in Table 2:

[0127] Table 2: Effect of cementing fluid concentration on the solidification of heavy metal contaminated soil

[0128]

[0129] As shown in Table 2, when the concentration of the cementing fluid is 0.5-1 mol / L, the unconfined compressive strength of the contaminated soil treated by microbial solidification is in a significantly increasing state, and the contaminated soil solidification effect is good. When the concentration of the cementing fluid is less than 0.5 mol / L or greater than 1 mol / L, the unconfined compressive strength of the contaminated soil treated by microbial solidification is greatly reduced; when the concentration is less than 0.5 mol / L, the amount of calcium source ions required by MICP is not met, so the calcium carbonate precipitation generated is too small, and the soil solidification effect is not good; when the concentration is greater than 1 mol / L, when the concentration of the cementing fluid increases, the loss rate of heavy metals also increases, resulting in unstable contaminated soil solidification and reduced soil strength values.

[0130] Example 6

[0131] Based on Example 1, this example tests the concentration of lead and zinc toxicity dissolved in the contaminated soil by microbial solidification treatment by adjusting the injection amount of the bacterial solution through indoor experiments, as shown in Table 3:

[0132] Table 3: Effect of the injection volume of bacterial solution on the toxicity dissolution concentration of lead and zinc in contaminated soil treated by microbial solidification

[0133]

[0134]

[0135] As shown in Table 3, according to the TCLP, the maximum limit of toxic dissolution of lead pollutants is 5 mg / L, and the maximum limit of toxic dissolution of zinc pollutants is 100 mg / L. When the injection volume of each bacterial solution is 1 to 1.5 times the pore volume of the soil, the toxic concentration of lead and zinc ions meets the prescribed limit, and the repair of heavy metal soil is effective. When the injection volume of each bacterial solution is less than 1 times the pore volume of the soil or greater than 1.5 times the pore volume of the soil, the bacterial solution cannot produce an appropriate amount of urease to catalyze the hydrolysis of urea, resulting in poor MICP repair of heavy metal contaminated soil, and the heavy metal toxicity cannot be well fixed in the soil.

[0136] Example 7

[0137] This example tests the concentration of lead and zinc toxicity dissolved in the contaminated soil treated by microbial solidification by adjusting the injection amount of the reaction solution through indoor experiments on the basis of Example 1, as shown in Table 4:

[0138] Table 4: Effect of injection volume of reaction solution on toxic lead and zinc dissolution concentration in contaminated soil treated by microbial solidification

[0139]

[0140]

[0141] As shown in Table 4, according to the TCLP, the maximum limit of toxic dissolution of lead pollutants is 5 mg / L, and the maximum limit of toxic dissolution of zinc pollutants is 100 mg / L. The toxic concentration of lead and zinc ions meets the prescribed limit, and the repair of heavy metal soil is effective. When the injection volume of each bacterial solution is less than 1 times the pore volume of the soil or greater than 2 times the pore volume of the soil, the calcium source ions in the reaction solution cannot fully react with the carbonate ions in the bacterial solution, and the migration of heavy metals cannot be effectively restricted.

[0142] By matching the indoor test device with the intelligent grouting device, the grouting process is consistent, and the above parameter results can be used for practical application and reference on site.

[0143] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for solidifying heavy metal contaminated soil based on nickel slag loaded microorganisms, characterized in that: The specific steps include: Step S1, culturing a Bacillus pasteurianus bacterial solution until the optical density OD600 value of the bacterial solution at a wavelength of 600 nm is 1.8-2.0; Step S2, dissolving 50-100 g of urea and 100-120 g of CaCl2 in deionized water, stirring evenly, to obtain a binder; the concentration of the binder is 0.5 mol / L-1 mol / L; Step S3, adding the screened nickel slag particles to the binder obtained in step S2, mixing the nickel slag particles and the binder according to a solid-liquid ratio of 2:1-3:1, adopting a "secondary static stop" method, stirring for 5-10 minutes, standing for 3-5 minutes, and performing secondary stirring to obtain a reaction solution; Step S4, injecting the bacterial solution and the reaction solution with an optical density OD600 value of 1.8-2.0 into the heavy metal contaminated soil through the intelligent grouting device in turn until the heavy metal dissolution value meets the specified limit, thereby completing the solidification of the heavy metal contaminated soil; The amount of bacterial solution injected each time is 1~1.5 times the pore volume of the soil sample, and the amount of reaction solution injected each time is 1~2 times the pore volume of the soil sample; The intelligent grouting device comprises: an underground grouting pipe (1), a soil pressure regulator (2), an underground connecting and distributing pipe (3), an aboveground connecting and distributing pipe (4), a peristaltic pump (5), a bacterial liquid storage tank (6), an aboveground valve button (7), a constant temperature control device (8), a reaction liquid storage tank (9), a liquid volume monitoring device (10), a base (11), a remote controller (13), an upper grouting pipe (14), a lower grouting pipe (15), and an underground valve button (16). The underground grouting pipe (1) is provided with a plurality of them, each of which is provided with a soil pressure regulator (2). Both sides of the underground grouting pipe (1) are provided with an upper grouting pipe (14) and a lower grouting pipe (15), and each of the upper grouting pipe (14) and the lower grouting pipe (15) is provided with an underground valve button (16). The top of the underground grouting pipe (1) is connected to the underground connecting and distributing pipe (3), and the underground connecting and distributing pipe (3) is connected to the aboveground connecting and distributing pipe (1). The bacteria liquid storage tank (6) and the reaction liquid storage tank (9) are connected to the aboveground connecting distribution pipe (4), the peristaltic pump (5) is arranged in the aboveground connecting distribution pipe (4), the bacteria liquid storage tank (6) and the reaction liquid storage tank (9) are respectively connected to the aboveground connecting distribution pipe (4), and an aboveground valve button (7) is provided at the aboveground connecting distribution pipe (4) connecting the bacteria liquid storage tank (6) and the reaction liquid storage tank (9), and the bacteria liquid storage tank (6) and the reaction liquid storage tank (9) are both provided with a liquid volume monitoring device (10), the peristaltic pump (5), the bacteria liquid storage tank (6), the constant temperature control device (8), and the reaction liquid storage tank (9) are all arranged on the base (11); the bacteria liquid storage tank (6) and the reaction liquid storage tank (9) are arranged in the constant temperature control device (8), and the remote controller (13) is respectively connected to the soil pressure regulator (2), the peristaltic pump (5), the aboveground valve button (7), the constant temperature control device (8), the liquid volume monitoring device (10), and the underground valve button (16); Step S4 specifically includes the following sub-steps: Step S401, starting the soil pressure regulator (2), the constant temperature control device (8), and the liquid volume monitoring device (10) through the remote controller (13); Step S402, adjusting the constant temperature control device (8) so that the temperature of the bacterial liquid and the reaction liquid is maintained at 1-5°C; Step S403, opening the underground valve button (16) alone to control the upper grouting pipe (14); Step S404, opening the above-ground valve button for controlling the bacterial solution separately, using a peristaltic pump (5) to inject the bacterial solution into the ground-inserted grouting pipe (1) and the upper grouting pipe (14) through the above-ground connecting distribution pipe (4) and the underground connecting distribution pipe (3), and controlling the amount of bacterial solution released through the soil pressure regulator (2). After the bacterial solution is injected, the solution is left to stand for 6 to 12 hours; Step S405, close the above-ground valve button for controlling the bacterial liquid, open the above-ground valve button for controlling the reaction liquid, use a peristaltic pump (5) to inject the reaction liquid into the ground-inserted grouting pipe (1) and the upper grouting pipe (14) through the above-ground connecting and distributing pipe (4) and the underground connecting and distributing pipe (3), and control the release amount of the reaction liquid through the soil pressure regulator (2). After the grouting is completed, let it stand for 12 to 15 hours; Step S406, closing the underground valve button controlling the upper grouting pipe (14), and opening the underground valve button controlling the lower grouting pipe (15) separately to change the grouting seepage direction; Step S407, open the ground valve button for controlling the bacterial solution separately, use a peristaltic pump (5) to inject the bacterial solution into the ground grouting pipe (1) and the lower grouting pipe (15) through the ground connecting distribution pipe (4) and the underground connecting distribution pipe (3), and control the release amount of the bacterial solution through the soil pressure regulator (2). After the bacterial solution is injected, let it stand for 6 to 12 hours; Step S408, close the above-ground valve button for controlling the bacterial liquid, and open the above-ground valve button for controlling the reaction liquid; use a peristaltic pump (5) to inject the reaction liquid into the ground-inserted grouting pipe (1) and the lower grouting pipe (15) through the above-ground connecting and distributing pipe (4) and the underground connecting and distributing pipe (3), and control the release amount of the reaction liquid through the soil pressure regulator (2); after the grouting is completed, let it stand for 12 to 15 hours; Step S409, repeating steps S403 to S408, taking soil samples on site, until the measured heavy metal dissolution value meets the specified limit, and turning off the intelligent grouting device through the remote control (13).

2. The method for solidifying heavy metal contaminated soil based on nickel slag loaded microorganisms according to claim 1, characterized in that: Step S1 includes the following sub-steps: Step S101, on a sterile operating table, inoculate Bacillus pasteurianus onto a solid culture medium, and invert the solid culture medium in a constant temperature box at 25-35° C. for culturing for 24-48 hours; each liter of the solid culture medium contains 10-20 g / L of tryptone, 1-5 g / L of soy peptone, 1-5 g / L of NaCl, 10-20 g / L of yeast extract, and 10-15 g of agar, and the pH of the solid culture medium is adjusted to 9.0-9.5 by 1-2 mol / L of NaOH solution, and the prepared solid culture medium is placed in a steam cooker at 120-130° C. for sterilization for 10-20 minutes; Step S102, selecting milky white colonies from the solid culture medium, adding them to the liquid culture medium, and shaking and culturing them at 25-30° C. until the optical density OD600 value of the bacterial solution at a wavelength of 600 nm is 1.8-2.0; the rotation speed of the shaking culture is 100-150 rpm; each liter of the liquid culture medium contains 10-20 g / L of tryptone, 1-5 g / L of soy peptone, 1-5 g / L of NaCl, and 10-20 g / L of yeast extract, and the pH of the liquid culture medium is adjusted to 9.0-9.5 by 1-2 mol / L NaOH solution, and the prepared liquid culture medium is placed in a steam cooker at 120-130° C. for sterilization for 10-20 min.

3. The method for solidifying heavy metal contaminated soil based on nickel slag loaded microorganisms according to claim 1, characterized in that: The process of obtaining the screened nickel slag particles is specifically as follows: (a) Wash the original nickel slag to remove impurities, dry it naturally, and store it in the open air for 1 to 2 months; (b) screening the original nickel slag with a square hole sieve with a diameter of 5 mm to remove nickel slag particles larger than 5 mm; (c) pouring the retained nickel slag into a particle crushing device, closing the device, and crushing for 5 to 10 minutes; (d) obtaining nickel slag particles with different crushing degrees, and packaging them according to particle size distribution through screening method, and retaining nickel slag particles with a particle size less than 0.25 mm.

4. The method for solidifying heavy metal contaminated soil based on nickel slag loaded microorganisms according to claim 1, characterized in that: The transverse grouting pipes extending from both sides of the underground grouting pipe (1) are 1.5 m long, the longitudinal upper grouting pipe (14) and lower grouting pipe (15) are both 1.0 m long, and the underground valve button (16) is arranged in the middle of the upper grouting pipe (14) and the lower grouting pipe (15).

5. The method for solidifying heavy metal contaminated soil based on nickel slag loaded microorganisms according to claim 1, characterized in that: The above-ground valve button (7) and the underground valve button (16) are electromagnetic automatic closing valve buttons.

6. The method for solidifying heavy metal contaminated soil based on nickel slag loaded microorganisms according to claim 1, characterized in that: The peristaltic pump (5) is a multi-cylinder high-pressure cross-flow peristaltic pump including an online detection system.

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